The objectives of this contract are: to determine if new antitumor drugs have biochemical mechanisms of action similar to those of clinically established antitumor drugs; to identify or provide clear leads to the biogically significant biochemical properties of new antitumor drugs; to select from among active structural analogs of clinically evaluated antitumor drugs, those which may have more desirable biochemical properties; and to develop and evaluate biochemical rationales for the combined use of clinically established antitumor drugs.